Producing and melting sponge iron



Aug. 1, 1933. A. E; GREENE FRoDUclN G AND MELTING PONGE IRON Filed July17, 1931 /l/ u/ N 7 Patented Ang. 1,- 1933 UNITED STATES .PAT'ENT-OFFICE 1,920,379 a PRODUCING AND MELTING SP ONGE IRON Albert E. Greene,Medina; wash.

Application 7 Claims.

An application has been filed in Canada June 18, 1925. My presentinvention relates to metallurgical process for the reduction of ore andparticularly to a combined treatment inwhich sponge iron is firstproduced and then collected in molten form. This application containssubject matter in 7 common with my applications for patent, Serial No.'726,541 filed July 17, 1924 (United States Patent No. 1,819,238) andSerial No. 34,041 filed June 1', 1925 (United States'Patent No.1,819,239).

'The object of my present invention is the production of molten iron orother metal by first responge iron was produced by heating a mixture ofcrushed iron ore 'and solid carbonace'ous material to areducingtemperature below the sintering temperature of the ore. This'wasdonein-a roiurnace. An

excess of 'carbbhaceous meten wasused. The

hot product was then coole'd andthe remaining v carbonaceous materialsubsequently separated.

This process has not proved commerciaL'as far a as is known, It hasanumber of disadvantages,

among which are the diiculty of preventing reoxidation of the fine ironand the difilculty of separatingthe excess carbon.. Even afterseparation, it has not proved practicable to liquefy the sponge ironthus produced; exceptby the process of my present invention.

- I have discovered a simple method of obtaining molten reduced ironfrom sponge iron which avoids the difiiculties just mentioned. I havefound that' I canproduce sponge iro'n by the above described process andthat the hot reduced iron mixed with carbonaceous material can befinished by passing this hot mixture into a hearth furnace on a bath'ofmolten slag which contains oxide of iron. The iron can then be collectedbeneath the slag while the carbonaceous matter can be kept above themetal and thus separated. I can in this way also remove any carbon whichmay have been, taken up by the reduced sponge iron, the'iron oxide ofthe slag 'combining with it. The process of my present invention may becarried out in any suitable apparatus, 'such for July 17, 1931, SerialNo. 551410, and in Canada June 18, 1925 p example, as a rotary kiln forproducing the reduced "sponge iron", together with a meting !ur nace,such as a furnace provided' with .electric heating means. However, theprocess ot the invention may be carried out in other apparatus.

Thus, the preliminary reduction may take place in any kind of suitablefurnace such as a roaster type furnace, and the product may be liqueiledin a reverberatory' type furnace using combustion heating. The preferredtype of apparatus is that shown in the annexed drawing, comprisingrarotary kiln for'reduction and an elongatd electri cally heated meltingfurnace equipped also tor p co'mbustion heating. g

ln thedrawingn Fig. 1 isa sectional elevation view showing a meltingfurnace and a. reducing 'furnace above the melting furnace, connectingwith the letter i V throughdischarge pipes which convey materials fromthe rotary'furnace into the melting furnace. This apparatus is acombination of my invention and may be employed for .carrying out .theprocess of this invention; and

Fig. 2 is a sectional elevation taken substantially along the line A- -Aof 1.

A brief description of this apparatus -wlllaid in u'ndefstanding .theOperations to be subsequently described heremm The melting chamber shownin section' in Fig. 1 is a; reverberatory i chamber having a hearthwhich slopes to the tap hole end of the chamber. The section is takenthrough the line' B.-B of Fig. 2. The refractory material is indicatedat 1. The rotary kiln type furnace is indicated at 2. It has a feed head3,

into which the material from the rotary furnace is discharged, and fromwhich it passes, through the pipes 4 and 5, into the melting chamber.Each pipe may be further provided with additional sections, as at 6 and7. 'Closing means or valves are also provided to control the flow ofmaterial into the melting furnace. These pipes open into the meltingchamber 'at locations 8 and 9 'and corresponding openings in the otherside of the roof.` A screw conveyor 11 serves to feed charge into theupper end of the rotary furnace through the stack 10. A fiue 12 isprovided in the end of the melting chamber for exit of gas, and a pipe13 into the feed head serves for entrance of gas and air for heating therotary furnace. In the lower end of the melting chamber hearth is a taphole for metal at 14. Metal is indicated at 15 and slag at 16, and aslag tap spout at 21. A burner is indicated diagrammatically at 17 forheating this chamber by combustion, and an opening at 22 is provided forthe 'content of the slag may controlled admission of air for combustionin the flue end of the melting chamber. A charge opening and entrancefor material is indicated at 18. An electrode 19 is shown for electricheating of the urnace, and other electrodes may be provided in line withthis one for heating the slag end of the chamber or elswhere for heatingthe whole chamber electrcally. I have shown a refractory wall 20 whichmay be provided in this chamber to separate the electric heating chamberfrom the remainder of the furnace.

I will now describe the operation of my process of this presentinvention for the reduction of iron ore. The production of sponge ironor finely reduced iron made without melting either the reduced iron orthe charge material is accomplshed by preparing a charge of fine ironore and carbonaceous material such as coal, the proportion of the latterbeing sufficient that some remains unconsumed after the operation in thefirst reducing chamber is completed. De-

pending on the grade and nature of the carbonaceous material, the exactamount in the charge `is determinedwth a View to having this materialpresent at the endof the rotary kiln operation. The amount may be asmuch as equal partsof ore and carbonaceous material although usuallymuch less carbon will serve. This charge is ed into the upper end of therotary kiln through the screw feed mechanism 11. The rotary kiln isheated by c'ombustion. Reducing gas may be admitted together with air,or air alone may be admitted to partly burn the carbonaceous material ofthe charge. The temperature is regulated so as not to form clinker orfuse the charge material, and ample time is allowed to permit reductionto the desired extent. The rotary kiln is set at a slight angle such aswill give the material the necessary time within the kiln in moving fromentrance .to exit end, and the speed of rotation is further controlledwith this end in View. It is understood that the angle of the rotarykiln is only illustrated diagrammatically in this drawing. The reductionof oxide of iron takes place at elevated temperatures approximatingthose at which sintering takes place and at temperatures below this downto about 500 C. The `rotary kiln discharges into the feed head 3 andfrom here the product from the rotary kiln is passed down through thepipes shown into the melting urnace. The product'from the rotarykilncontains reduced iron in small particles together with carbonaceousmaterial andthe re- `rnaining unreduced material of the ore original lycharged. This product is passed into the melting furnace on the moltenslag covered bath. Here it is heated in a pile which graduallyeliminishes except as it is replenished by further entering charge fromthe rotary furnace. The charge on the slagis heated gradually and thereduced iron passes down through the slag and then into the molten bathbeneath. The excess o! carbon is retained on the slag and may beoxidized by the admission of air and/ or by reaction with the oxide ofiron in the slag, but it is necessary to maintain a small percentage ofoxide of iron in the slag in order to counteract or remove any carbontaken up by the reduced iron during the previous treatment. Thus, myprocess provides for dropping the hot reduced iron and other material ona slag bath containing iron oxide which will react with carbon present.This oxide be provided either by addition of iron oxide to wisemaintaining conditions in the chamber the slag or by otherv which causethe oxide to form in limited amount. I may add a portion of oxide ofiron with the charge which enters from the sponge furnace.

The action which results is the collection of the carbonaceous materialon the molten slag and the passage down through that slag of the reducedsponge iron.` The oxide of iron in the slag serves to de'carbonize thereduced iron and the result is the formation of low carbon iron beneaththe slag. It is possible to control this .reaction so as to obtain asmaller or a greater percentage of carbon in the reduced and liquefiediron beneath the slag, and this may be done by maintaining a greater ora smaller amount of oxide of .iron in the slag. The actual percentagemay be within the limits between a few percent and as much astwenty-flve percent of iron oxide in the slag. The excess carbonaceousmaterial entering with the sponge iron can be utilized in the meltingfurnace to provide heat by admission of air. However. I do not limit mymethod to either an electric or any other kind of melting Iurnace. i i

What I claim is:

1.` The method o! producing molten iron from iron oxide material whichcomprises reducing the iron oxide at a temperature below the sinteringpoint of the material in the presence of an excess of carbonaceousmaterial, passing the resulting product containing reduced iron togetherwith carbonaceous matter and unreduced material into a melting furnace,and collecting the reduced metal in molten condition beneath a slagcontaining oxide of iron in sufficient quantity to prevent' theremaining carbonaceous material from entering-the molten metal beneath.

2. The method of producing iron from iron oxide ore which comprisesreducing the iron oxide by means of carbonaceous material in a reducingchamber ,at a temperature below the fusion point of the ore, passing theproduct from this furnace while hot and while retaining solidcarbonaceous material in excess into a melting chamber on a molten slagbath, melting the reduced iron on the slag in the presence of iron oxideto form particles which pass down into and through the molten slag, andcollecting the molten iron beneath the slag.

3. The method of producing iron from iron oxide' ore which comprisesreducing the oxide of iron at a relatively low temperature below thesintering temperature of the ore, using solid carbonaceous material inexcess of the amount required to reduce the oxide, and without coolingthe product or separating the excess carbonaceous material, passing thecharge onto a molten bath covered with slag containing oxide of iron andthere 'melting the reduced iron and collecting it beneath the oxide slagwithout permitting the excess carbon to carbonize the metal beneath theslag. v 4. The method oi reducing and melting ironwhich consists intreating an iron oxide ore with carbonaceous material in excess of theamount needed for reduction to reduce the oxide without melting it, andthen passing the hot material containing reduced iron, unreduced earthymaterial and carbon into a melting chamber and there causing the reducediron to pass down through* a slag containing oxide of iron butpreventing carbon from passing through this slag.

5. The method of treating oxide of iron to reduce it which consists infirst producing sponge iron by reducing the iron oxide material withcarbonaceous material in a 'educing chamber beconsists in firstproducing sponge iron in a reducing chamber without fusion of thematerial therein and while retaining this product hot and in thepresence of solid carbonaceous material to prevent reoxidation, passingit into a melting chanber onto a bath covered with a slag con tainingoxide of iron. melting the reduced iron and collecting it beneath thesiag, and oxidizing the remaining carbon by means of oxide in the slagand combustion above it.

'7. The method of producing liquefied iron which method comprises firstproducing sponge iron in the presence of an excess of carbonaceousmaterial, passing the resulting sponge iron and remaining carbonaceousmaterial into a melting furnace on a moltenslag bath, maintaining ironoxide in the slag while melting the sponge iron and collecting lowcarbon iron molten beneath said slag.

ALBERT E. GREENE.

